Telephone substation circuit



March 11, 1947. A, FAR LLA 2,417,067

TELEPHONE SUBSTATION CIRCUIT Filed March 10, 1945 2 Sheets-Sheet l TO COIL I6 TO KEY3O TO COIL I6 TO KEY 30 4OXL TO COIL l6 T0 KEY 30 I TO COIL IS TO KEY 30 0 0O 2 4O].k

RESISTIVE L'INE 38-40 COMPONENT OF l8 INVENTOR. RAOUL A. FARALLA ATTORNEY March 11, 1947. R AR 2,417,067

TELEPHONE SUBSTATION CIRCUIT Filed March 10, 1945 2 Sheets-Sheet- 2 FIG.8

INVENTOR. RAOUL A. FARALLA Zxea QM ATTORNEY tion circuits, these means Patented Mar. 11 1947 UNITED STATES PATENT,

OFFICE The invention described herein may be manufactured and used by or for the Government for governmental purposes, withoutthe payment to me of any royalty thereon.

This invention relates to substation telephone circuits, and, particularly, to portable field telephones and substation circuits which, because of the use to which they are subjected, may be connectedto lines of greatly varied lengths.

It is well-known in the art that the sensitivity of the magnetic sound-powered receivers is superior to the sensitivity of the receivers of stand ard type, the output level of the souncl-powered receivers being from 12 to 16 db. higher than of the electromagnetic receivers, and, therefore, it is especially desirable to use such receivers in connection with the field telephone substations, such as Army Signal Corps'substations, since the superior sensitivity of such receivers makes it possible to extend the range of the field telephone communications. However, when receivers of this type become connected to lines of relatively short length, the intensity of the signal impressed upon them is so high thatthe output of the receiver becomes too loud, and, in extreme cases, the receiver becomes overloaded to such an extent that its articulation quality is impaired and the speech becomes almost unintelligible. Moreover, when sound-powered receivers are substituted for receivers of standard type, they reproduce cross-talk and noise signals with such a degree of loudness that the signal-to-noise ratio is impaired, and the cross-talk signal interferes with the desired speech'signal. This disadvantage disappears when the sound-powered receiveris connected to long lines, because'the noise and cross-talk Signals become attenuated to such an extent that the receiver clearly reproduces only the desired signal. I

In order to obtain the same degree of clarity of the desired signal when receivers of this type are connected to lines of short length, it becomes necessary to reduce their sensitivity, and the invention discloses several methods of accomplishing this result.

According to the disclosed methods, the number of effective turns of the coil of the receiver may be varied, thus decreasing the transmitting efiiciency of the receiver, and, at the same time,

.creating the mismatched impedance condition in the substation circuit which, in itself,'acts as a means for reducing the efliciency of the substation circuit, Mechanical means are provided for altering the connections in the substataking the form of amended April 30, 1928; 370

altering the number of eifective either a switch era-revolving knob which is used for varying the degree of attenuation and impedance mismatchin-the receiver circuit.

It is, therefore, a principal'object of this invention to provide a means for controlling the sensitivity of'sound-powered receivers by reducing thenumbenof effective ampereturns in the receiver circuit; and by'mism'at'ching its impedance with respect tofthe impedance looking away from the receiver, the impedance of the receiver normally matching the impedance of the outgoing circuit for obtaining maximum sensitivity of the receiver when it is connected to long transmission lines. I

The novel features which are believed to be characteristic ofthis invention-are set forth with particularity in. the appended claims. The invention itself, however; both as to its organization and method-of'operation, together with the further object and advantages thereof, may best be understood by reference to "the following dethe accompanying drawings in which: a T

Figure 1 is a schematic diagram of a portable substation circuit of the local battery type, in

which the sensitivity of the receiver is varied by turns in the coil of the receiver;

Figures 2 to 5 are schematic diagrams of the receiver and balancing circuit disclosed in Fig. 1,--in which the sensitivity of the receiver and mismatching of the impedances is accomplished by means of resistance elements, and

w Figure 6 is an equivalent schematic diagram of the substation circuit shown in Fig. 1.

Figs. '7' and 8 illustrate two plan views of a handset and one of the methods of mounting the sensitivity-selectingswitch, with the receiver and. transmitter removed and a side view of the switch assembly being illustrated in Fig. 8.

- Referring to Fig.1, it'discloses one of the most desirable types of substation circuits for local battery-use, which is known in the United States telephone industry as U. S; Army telephone It inoludesra'transmitten ID, a receiver l2, an iiiduction' coil, or an autotransformer having coils i4, i6 and I8, isolating condenser 20, a reactance balancing condenser 22, a ringer 24, a

"hand generator 26, a ringing circuit switch 28, a

transmitter switch 30, and a receiver switch 32. Hand generator 26 is usedfor ringing purposes, whose cranking handle is coupled through a cam to switch 28,"so as totransfer this switch toa contact 33 "at the-beginning "of the ringing operation, -switchf '28 normally rests on contact 34 which is connected to ringer 24, the circuit of which is completed through a condenser 36. The outgoing line conductors 38 and 40 are connected across the induction coil through condensers 22 4 cuit, while, when switch 32 rests on contact 52, only the lower portion 50 of the receivers coil is effective, and, aS a consequence, by operating switch 32 the sensitivity of the receiver may be and 20, and transmitter I is of standard, car- 5 controlled by selecting either one of the two availbon type. It is connected across the primary able sensitivities. winding IB of the autotransformer, a local source Examination of Fig. '7 reveals .the fact that if of potential 42 supplying the necessary power for the impedances and the ampere turns in the the transmitter. Parasitic discharge of source autotransformer are so adjusted that the poten- 42 where switch 30 is closed is prevented by in- 'tials appearing at points 100 and 102 of the serting the condensers 20 and 22 in the balancing Wheatstone bridge are equal when transmitter 50 and line circuits, respectively. Transmitter impresses the varying direct current of predeswitch 30 is provided for disconnecting the transtermined frequency on primary I6 of the auto mitter, and especially battery 42, from the pritransformer, no current will flow across the windmary winding IE to prevent unnecessary dising of receiver l2. As mentioned previously, this charge of battery through the primary when the is the case in the idealized substation circuit, and transmitter is not in use. The secondary windin the practical substation circuits there 15 a ings l4 and N3 of the autotransformer are conpresence of some side-tone current in the receiver nected to the conductors of the outgoing line, as during the transmitting cycle. If the impedance mentioned previously, winding l8, in combination. of receiver I2 is varied, as is the case with the with condenser 20, forming a balancing network receiver illustrated in Fig. 1., such variation of of the substation circuit, the .impedance and the. the receiversimpedance will have no eiTect on number of turns of this balancing network being the balanced condition of the substation circuit so adjusted as to act as an anti-side-tone device during the transmitting cycle. Accordingly, the during the transmitting cycle. The substation 25 sensitivity of the receiver may be adjusted to any circuit disclosed in Fig. 1 may be shown in a simdesired extent without impairing the normal piified form so as to re resent a balanced. A, C. functioning of the anti-side-tone feature of the Wheatstone bridge as illustrated in .Fig. '7, the circuit. respective components of the substation circuit During the receiving cycle the current will flow being similarly numbered in both figures. As is through the sound coil of the receiver l2, and, wellkn'own in the art. the circuit, theoretically, depending upon the position of key 32, either the is des gned to satisfy the condit ons for no curentire coil or only a small portion of it W111 be rent in the receiver with an E, M. F. in the transincluded in the circuit of the receiver. This cirmitter. and for no current in the bal ncing netcuit, as illustrated in Fig. 1, includes conductor work Iii-20 when there is an E. M. F, in the 45!,condenser 22, conductor 46, coil 50,spring conline. Actual circuits do not strictly satisfy these tact 52, SW h conductor p ry conditions for an of the different line conditions secondary d conductor n the ideehzed and frequencies, so that in actual substation cir circuit no current will flow through the balanccuits there is always a small current flowing in ing networks I8 and 2|] when receiving, because the receiver when. transmitting. and a small curof t pp s n p t al generated y the se rent flowing in the balancing network when reondaly h e key in the full sensitivity ceiving The disclosure neednot b b d position, the entire coil of the receiver is included with a d scussion of the anti-side-tone features in the previous y traced Circuit, a d With the im of the substation circuit. since it is well-known pedance of the receiver matching the Impedance in the art, and is fully dis by G, Campof the outgoing circuit, half of the available power bell and R. M. Foster in the Transactions of the A. I. E. E.. vol. 39, pp. 231-290. As demonstrated in the above mentioned article, theimpedance of receiver l2, in order to obtain the optimum utilization of power, must be equal to t e imp dance of the outgoing circuit when looking from the termin ls of the receiver. Accordingly, the impeda ce of the sound-coil of receiver I2 is equal to the equivalent impedance measured across the conductors '44 and 45 which connect the receiver to this impedance, This impedance includes the impedance of the outgoin line and the terminal apparatus on the other side of the line, if the impedance of the line is smaller than the ch racteristic impedance.

In the disclosed circuit the standard electroma netic receiver has been replaced'wit'h a magnetic. sound-powered receiver, and the receivers coil has been tapped so as to have a larger number of turns in that portion of the .coil which is designated by numeral 48, and a smaller number of turns in the portion designated by .numeral 50. In one particular receiver the number of turns in portion is 7'7, and in the other portion 463. The tap is connected to a s ring con-. tact 52 of the volume controlswitc'h 32, the other end of the same coil being connected to a spring 54 of the same switch. When switch 32 rests on .contact 54, the entire winding of the sound-pow: ered receiver is connected in the substflimn G ffwill be available in the receiver itself, which is the maximum sensitivity condition obtainable.

Figs. 2 to 5 disclose additional impedance-mismatching modifications and circuits for reducing 50 the effective number of turns in the circuit of the receiver which accomplish the sought result by means of shunt or series resistances of fixed or variable values. Only the balancing leg I820, condenser I5, and coil i2 of the receiver are 55 shown in Figs. 2 to 5, since the remaining elements of the substation circuit are identical to those shown in Fig. 1 the dotted line AA indicating the line along which Figs. 2 to 5 should be connected to the substation circuit shown in Fig. 1.

In Fig. 2 a fixed resistance element 200 is connected to key 32, and when key 32 is connected to contact 54 maximum sensitivity of the receiver is obtainable. When key 32 is connected to contact 52, the coil of the receiver I2 is connected in series with resistance 200, and, as a result. the receiver has lower sensitivity.

In Fig. 3 the same .result is obtained by means of a variable rheostat 300 which, when in zero resistance position, allows the receiver to 0perate at its maximum ampere turn efiiciency. No switching key is required in Fig. 3, and the senziggvity is adjusted by means of the rheostat arm Fig. .4 discloses an arrangement where the coil et the receiver is'shunted bymeans of a resistance 400, and 'key 402 is Operated to obtain lower sensitivity of the receiver. In Fig. 5 the same result is obtained by shunting the balancing network [8-20 bymeans of variable resistance 500. This resistance may be a fixed resistance with a key, if so desired.

Figs. 4 and 5 disclose identical circuits from jthe point-of view of the effectiveness of control, except that 'whilein Fig. 4 resistance 400 is placed in the handle of the receiver, in Fig. 5 resistance 50!] is placed in the portable box including the substation circuit itself. 7

The disclosed control of the sensitivity of the receiver may be accomplished by replacing resistance 300 in Fig. 3 with a variometer or an inductance coil with an adjustable iron core. These modifications are not illustrated in the drawing because they are'less effective in accomplishing the sought result than the illustrated circuits. Figs. 7 and 8 illustrate a telephone handset '60 equipped with a dual sensitivity switch 6:! which may be either of butterfly or knob type. Conductors 6 2, 63 and 64 in Fig. 8 correspond to conductor 46 and two jumpers connecting the coil to contacts 52 and 54. j While the invention has been described with reference to several particular embodiments, it will be understood that various modifications of the apparatusshown may be made within the scope of the following claims.

I claim: U 1. In a substation circuit, a line,' an auto-transiormer having first, second and third serially connected windings, a receiverhaving a switch,-for manually controlling the sensitivity of said receiver, said receiver being connected in series with said first and second windings and the conductors of said line, a condenser connected between said third coil and said receiver, said condenser and said third coil forming an anti-side-tone circuit serially connected transmitter and a local battery connected across said second windingand means, including said switch, for varying the number ofeffectiveampere turns in said receiver.

2. In a substation circuit, a line, a transformer having first, second and third serially connected windings, a receiver having a volume control switch, said receiver being :connectedin series with said first and second windings and the conductors of said line, a condenser in serial relation withjsaid third winding, said condenser and said third winding forming an anti-side-tone circuit "connected across said receiver, a transmitter connected in shunt of said second winding of said transformer, a winding in said receiver, and

means including said volume control switch for at will including all the ampere turns of said receiver winding or only a portion of said ampere turns in said receiving circuit.

3. In a substation circuit, a line, a transformer having first, second and third serially connected windings, a condenser connecting said third winding to a line conductor, said condenser and said third winding forming an anti-side-tone network of said substation circuit, a handset including a transmitter and a receiver, said receiver being connected across said network, a volume control receiver switch and a transmitter key mounted on the handle of said handset between the receiver and transmitter, a series receiving circuit including said switch, receiver, first and second windings and the conductors of said line, a series transmitter circuit including said key, transmitte'rgand said second winding, said key providing means for at will opening and closing said transmitter circuit, and means including said switch for at will including all or only a, por- 5 tion of the normally available ampere turns in said receiving circuit.

4.. In a substation circuit, a line, a transformer having three windings, a handset including a transmitter and areceiver, a volume control receiver switch mounted on the handle of said handset between said transmitter and receiver, a receiving circuit including said switch and receiver connected in series with a first and a second winding of said transformer and the conductors of said line, a third winding of said transformer and a condenser in serial relation connected in shunt of said receiver to form an anti-side-tone circuit, a transmitter circuit including said trans' mitter connected in shunt of said second winding of said transformer, a winding in said receiver, and means including said switch for including at will all or only a portion of the normally available ampere turns in said receiving circuit. I I I 5. In a substation circuit, a line, a transformer having first, second'and third windings, 'a condenser connecting said third winding to a line conductor, said condenser and said third winding forming an anti-side-tone network of said substation circuit, a transmitter connected across said second winding, a receiver having three terminals, a receiver winding connected between said first and third terminals, a tap connection extending from said second terminal to means for varying the number of efi ective' ampere turns of said Winding, a volume control receiver switch having connections to said second and third terminals and means for switching between said connections for including either the maximum or only a portion of the receivers ampere turns.

6. In a substation circuit, a line, a transformer having three windings, a receiver having a winding of a plurality of turns between receiver terminals, a connection extending from one of the terminals of said receiver winding, 2. volume control receiver switch having means for switching between one of said receiver terminals and said connection anda receiver circuit including said switch, said switch connecting either the entire 50 winding ofsaid receiver or only a portion of the normally effective ampere turns of saidrreceiver.

7. In a substation circuit, a line, a transformer having three windings and'a'condenser connected in series in bridge of the line conductors of 55 said lineka transmitter connected in bridge of one of saidwindings, 'a 'receiver' connected in bridge of said condenser and another of said windings, said receiver having a windingwhose impedance matches the normal impedance of 60 said substation circuit at the points where said receiver is connected into said substation circuit, a connection extending from a point in said receiver winding, a first receiver circuit including the entire receiver winding thereby matching the impedance of the receiver with respect to said substation circuit to secure the greatest output level from said receiver in response to incoming signals, a second receiver circuit including said connection and said receiver 7 winding thereby mismatching the impedance of the receiver with respect to the impedance of said substation circuit to introduce a loss in the output level from said receiver in response to incoming signals of the same strength as were received in said first receiver circuit, and a switch- ,ing key forswitching the substation circuit at will from one-of said receiver circuits to the other 0f said receiver circuits dependent upon the ceiver winding, a first receiver circuit including the entire receiver winding thereby making the impedanc of the receiver with respect to said substation circuit to secure the-greatest output level from said receiver in response to incoming ;signals, a second receiver circuit including said connection and said receiver winding thereby mismatching the impedance'of the receiver circuit with respect to the impedance of said substation -circuit to introduce ;a loss in the output level from said receiver in response to incoming signals of the same strength as were received in said first receiver circuit, and a switching key for switching the'substation circuit at will from one of said receiver circuits to the other of said receiver circuits dependent upon the output level desired from said receiver.

- 9. In a substation circuit, an autotransformer .having first, second, and third serially-connected coils; first and second condensers connected in series between a first line conductor and said first coil; a .magnetic, sound-powered receiver with its winding connected across said first condenser and said first coil; a second line conductor connected to the outer terminal of said third coil whereby the receiving circuit of said substation circuit is through said second condenser, winding of the receiver, and second and third coils of said transformer, the impedance of said winding of the receiver matching the equivalent impedance looking away from said receiver; a local battery transmitter circuit connected across the second winding of said transformer, whereby said first coil and said first condenser ,act as an anti-side-tone circuit of said receiver,

and a resistance element connectable across said anti-side-tone circuit for varying the effective ampere turns of the winding of said receiver.

10. In a substation circuit, an autotransformer having first, second and third serially-connected coils; first and second condensers connected in series between a first line conductor and said first coil; a magnetic, sound-powered receiver with its winding connected across said first condenser and said first coil; a second line conductor connected to the outer terminal of said third coil whereby the receiving circuit of said substation cir- -cu-it isthroug-h said secondcondenser, winding of the receiver, and second and third coils of said transformer, the impedance of said winding of the receiver matching the equivalent impedance line having characteristicimpedance.

11. A telephone handset including a receiver, a

.receiver circuit connected to said receiver, a transmitter, a transmitting circuit connected to said transmitter and means within said handset for varying the amount of energy applied to the receiver, and amanuallyoperable control device on'theexterior-of said handset to which said means is responsive.

12. In a device of the class described, a handset including a transmitter and a receiver, a volume control device for varying the sensitivity of the receiver, said control device being mounted on said-handset casing between the transmitter and the receiver; a receiving circuit, and means associated with said control device for varying the output of said receiver, said means being responsive to operation of said control device.

13. A telephone handset including a receiver equipped with a dual sensitivity control device, a receiver circuit connected thereto, a transmitter adapted to be connected to a transmitter circuit, means within the receiver circuit for causing the impedance of the receiver to match the impedance of the telephone circuit looking away from said receiver or for at will causing the impedance of the receiver to mismatch said impedance, and a manually operable switch for controlling said means whereby the level output of the receiver may be varied at will.

-- RAOUL A. FARALLA.

REFERENCES CITED The following references are of record in the file of this patent:

v UNITED STATES PATENTS Number Disclaimer 2,417,067.Ra0ul A. Faralla, Long Branch, N. J. TELEP Patent dated Mar. 11, 1947. Disclaimer filed M Hereby enters this disclaimer to claims 7 and 8 in s [Oficial Gazette June 21, 1.949.]

HONE SUBSTATION: CIRCUIT. ay 4, 1949, by the inventor. aid specification. 

